Filters comprising a base made of acetate-cellulose fibers in combination with charcoal are known in the art. The charcoal can be contained in the base as mechanical inclusions, may form a coating on the base or simply be in contact with it. A drawback of these filters is that they do not completely eliminate the harmful effect of a number of the carcinogenic and toxic components of tobacco smoke.
In view of this, effective filtration means are needed which remove as much as possible a large amount of the harmful components of tobacco smoke, but permit its organoleptic characteristics to be preserved.
Also known is another cigarette filter made from hydroxyapatite in combination with acetate fibers or activated charcoal. The hydroxyapatite may be represented by the formula EQU 3[Ca.sub.3 (PO.sub.4)]M(OH).sub.2,
where M is a cation of calcium, strontium or lead.
Generally, hydroxyapatites are used in which the M-cation is calcium, since this material is not toxic, and is highly effective. The hydroxyapatite is a material having a particle size of from 2 to 5 .mu.m and is used in the filter in an amount of from 0.1 to 20% of the tobacco weight in the cigarette. This filter can be made in the form of a tablet, sleeve, mouthpiece, etc. The filter ensures an improved absorption of harmful substances, such as nicotine, tar, carbon monoxide, from the tobacco smoke. However, it does not facilitate the absorption of carcinogenic and toxic substances, such as the polycyclic aromatic hydrocarbons benzo(a)pyrene, benzo(g,h,c,)perylene, dibenzo(a,h)anthracene, dibenzo(a,c)anthracene and volatile nitrosoamines (N'-nitrosodiethylamine, N'-nitrosopyrrolidine), from tobacco smoke.
Various cigarette filters are known which decrease the toxic effect of tobacco smoke. These consist of a base made of acetate, cellulose or acetate-cellulose fibers with substances applied unto the base which have adsorption properties or are impregnated with these substances.
Activated charcoal, inorganic and organic slats of mercaptoalkanesulfonic acids (cysteine, acethylcysteine and phthalocyanins) are used as the adsorbing agents.
A drawback of these filters is that the range of substances absorbed by them is restricted. The filters themselves can degrade on heating, which is accompanied by the formation of toxic compounds. Thus, for example, the utilization of phthalocyanine as a sorbent may result in the formation of the following products of decomposition: organic cyanides, ammonia, benzene derivatives, etc.
A filter is also known (see U.S. Pat. No. 5,083,579, of Jan. 28, 1992) comprising a base made of acetate, cellulose or acetate-cellulose fibers, and an absorbing substance which is a complex compound of bivalent iron and a ligand, which is a thiol containing low-molecular weight compound. In that compound the ratio of the iron ions to the number of ligand molecules is not greater than 1:2, while the amount of the absorbing substance is from 3 to 13% of the total weight of the filter.
In this filter the sources of bivalent iron were usually the salts of iron for example, FeSO.sub.4, FeCl.sub.2 and, Fe(NO.sub.3).sub.2. Monothiol-containing compounds (sodium thiol-sulphate, cysteine reduced gluthatione, etc.) and dithiol-containing organic compounds (diethyldithiocarbamate, dimethyldithiocarbamate, sodium ethylxanthate, etc.), were used as the thiol-containing low-molecular compounds.
The described filter makes it possible to efficiently clean the tobacco smoke of nitrogen oxide, but it does not, just like all the filters described, reduce the content in the tobacco smoke of such carcinogenic and toxic substances as polycyclic aromatic hydrocarbons (benzo(a) pyrene, benzo(g,h,i) perylene, dibenzo(a,h) anthracene, dibenzo(a,c) anthracene, volatile nitrosoamines (N'-nitrosodiethylamine, N'-nitrosopyrrolidine) as well as such metals as magnesium, calcium, strontium, copper, lead, arsenic, vanadium, chromium, manganese, iron, cobalt and nickel.
An acetate-cellulose filter is known comprising 10% triacetine as the adsorbing substance (see Williamson J. T. et al "The modification of cigarette smoke by filter tips", Betr. Tabakforseh., 1965, Bd.2, p. 233-242).
This filter selectively absorbs carcinogenic N-nitrosocompounds:
N-nitrosodiethylamine up to 75%, N-nitrosodiethylamine up to 50%, PA1 N-nitrosopyrrolidine up to 74%, tar up to 35%, nicotine up to 28%.
A drawback of this filter is that in practice it does not absorb benzo(a) pyrene and carcinogenic metals.
The filter most similar to the present invention is the cigarette filter comprising a base made of an acetate, cellulose or acetate-cellulose fiber, impregnated with an adsorbing substance which is a solution of an organo-silicon monomer N, N'-bis(3-triethoxysilylpropyl)-thiocarbamide (C.sub.2 H.sub.5 O).sub.3 Si(CH.sub.2).sub.3 NH - C(S)-NH(CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3, the amount of which is from 6 to 15.3% by weight of the weight of the base (see the publication of the application for European patent No. 0 493 026 of Jul. 1, 1992).
Standard cigarette filters are impregnated with a 4-10% solution of the mononer in a solvent, preferably in hexane, and convectively dried at 60.degree. in a thermostat.
This cigarette filter makes it possible to catch the carcinogenic and toxic substances, in particular, carcinogenic metals, N-nitrosocompounds and benzo(a)pyrene, better than known cigarette filters.
However, a drawback of this cigarette filter is that in respect of the absorption of carbon monoxide, nicotine and tar, it does not differ from known cigarette filters, and furthermore, it does not completely catch the N-nitrosocompounds.
The known cigarette filters described above do not as a whole reduce the amount of carcinogenic compounds in the mainstream of tobacco smoke by more than 50%, and each of the known filters is only capable of reducing the amount of a certain class of chemical compounds having carcinogenic and toxic properties. Therefore, a problem remaining in the existing filters is to reduce the level of the carcinogenic benzo(a)pyrene, carcinogenic metals, volatile N-nitrosocompounds, tobacco-specific N-nitrosocompounds, and also carbon monoxide, tar and nicotine, which would make it possible to reduce the risk of falling ill with malignant growths and other illnesses related to cigarette smoking.
The object of the present invention is to improve the amount of carbon monoxide, tar, nicotine, carcinogenic benzo(a)pyrene, carcinogenic metals, volatile nitrosocompounds and tobacco-specific N-nitrosocompounds removed from tobacco smoke.